Multi-layer reflective thin film filters optimized for oblique incidence angles were deposited on glass substrates using Electron Beam evaporation technique with in situ thickness monitoring. The present study involves deposition and optical characterization of 5 layered multi-layer structures of TiO₂-Al2O₃ and TiO₂-SiO₂ having different thicknesses for varied wavelength ranges in the visible region. Three TiO₂-SiO₂ multi-layer thin film filters were deposited having peak reflectance at 480 nm, 540 nm and 675 nm respectively corresponding to light sources in the blue, green and red wavelength regions. Similarly, a TiO₂-Al2O₃ multi-layer was fabricated having peak reflectance of around 64% at 610nm. These filters were deposited at an elevated temperature of 250° C in an oxygenated reactive environment for better adhesion, mechanical strength and proper stoichiometry. Reflectance measurements of these multi-layer filters at oblique incidence angles reveal high reflectance of around 70 ~ 75% with a reasonably broad reflection band which can have wide applications in beam steering, shaping and folding applications in various complex optical systems facing constrained space and weight requirements.

Date Published: 15 June 2015
PDF: 5 pages
Proc. SPIE 9654, International Conference on Optics and Photonics 2015, 96540F (15 June 2015); doi: 10.1117/12.2181776

Published in SPIE Proceedings Vol. 9654:
International Conference on Optics and Photonics 2015
Kallol Bhattacharya, Editor(s)